1. Field
This disclosure relates to a positive active material for a rechargeable lithium battery and a rechargeable lithium battery including the same.
2. Description of the Related Art
Recently, as a result of reductions in the size and weight of portable electronic equipment, there has been a need to develop batteries for use in smaller and lighter portable electronic equipment where the batteries have both high performance and a large capacity.
Batteries generate electric power using an electrochemical reaction material (referred to hereinafter simply as the “active material”) for a positive electrode and an active material for a negative electrode. Rechargeable lithium batteries generate electrical energy from changes of chemical potential during the intercalation/deintercalation of lithium ions at the positive and negative electrodes.
Rechargeable lithium batteries use materials that reversibly intercalate or deintercalate lithium ions during charge and discharge reactions for both positive and negative active materials. Rechargeable lithium batteries may contain an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.
For positive active materials that can be in a rechargeable lithium battery, lithium composite metal compounds have been used, for example, lithium composite metal oxides such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), LiMnO2, or the like have been researched.
Of the positive active materials, manganese-based positive active materials such as LiMn2O4 or LiMnO2 are generally the easiest to synthesize, are less costly than the other materials, have better thermal stability than other active materials during overcharging, and are generally environmentally friendly. However, these manganese-based materials have relatively low capacity.
Among the commercially available positive active materials, LiCoO2 is representative, as it has good electrical conductivity, a high battery voltage of about 3.7 V, good cycle-life characteristics, high stability, and good discharge capacity. However, as LiCoO2 is expensive (e.g., it may be 30% or more of the total cost of a battery), it has disadvantages in terms of cost.
Also, LiNiO2 has the highest discharge capacity characteristics among the above referred positive active materials, but it is difficult to synthesize. Further, the high oxidation states of nickel cause battery and electrode cycle-life deterioration. Batteries including LiNiO2 often self-discharge and have lowered reversibility. Furthermore, it is difficult to fabricate commercially available batteries including LiNiO2 as it is difficult to ensure stability.